This invention relates to emission controls for vehicles powered by internal combustion engines and in particular to the filtering of particulates from engine exhaust gases and more specifically, to the periodic incineration of the collected particulates in the filter through a temporary increase in the exhaust gas temperature by backpressuring of the engine.
Federal and State governments have adopted stringent new standards for particulate emissions for all diesel powered road vehicles. These new standards necessitate a device in the diesel engine exhaust system for removal of the particulates. Such exhaust treatment systems typically consist of a particulate trap to collect particulates from the exhaust gas stream during engine operation. Such particulates consist largely of carbon and heavy hydrocarbon particles which, with continued operation, tend to plug the exhaust filter, causing a restriction to the normal exhaust gas flow. Periodic cleaning of the particles from the exhaust gas filter is required in order to avoid the increase in the engine exhaust backpressure which adversely affects the fuel economy and vehicle performance.
In order to burn the filtered particulate it is necessary to increase the exhaust gas temperature in the filter or trap. Under typical operation, diesel engine exhaust temperatures high enough to burn the particulate are not experienced for sufficient time periods to clean the trap. Therefore, either a separate device is required to provide sufficient heat to burn the accumulated particulates or a separate means of obtaining increased exhaust gas temperatures must be found.
One means for increasing the exhaust gas temperature is to use a burner upstream of the filter. This may be accomplished by any practical burner mechanism such as the mechanism disclosed in the copending U.S. patent application Ser. No. 794,346, filed on Nov. 1, 1985 and entitled "Diesel Engine Particulate Trap Regeneration System". However, burners have several disadvantages, which include the use of additional fuel, the pumping transport and injection of that fuel and the general problems of stable combustion at low pressures.
The present invention has been developed to eliminate the need for a burner device to be used in cooperation with the particulate filter. According to the apparatus of the present invention, a particulate trap regeneration system used in association with a turbocharged or naturally aspirated engine comprises an exhaust gas particulate trap within the engine exhaust system downstream of the engine, a backpressuring valve within the engine exhaust gas flow downstream of said engine, an actuator to control the movement of the backpressure valve and a microprocessor for receiving relevant engine operating parameters from sensors and controlling the actuator. Under normal operating procedure, the backpressure valve remains in a wide open position. However, when the particulate trap pressure drop reaches a value indicating a significant amount of particles are present, as sensed by the microprocessor, the backpressure valve is partially closed. At this time the microprocessor activates the actuator to close the valve, thus increasing the particulate trap temperature; which in turn allows oxidation of the trapped debris.
It is an object of the present invention to provide a diesel engine particulate trap and regeneration system in order to reduce pollution.
It is another object of this invention to provide an improved system for controlling the regeneration cycle of the particulate trap. The resulting system will cause a minimum performance and efficiency loss to the engine and will be mechanized in a simple and reliable manner.
It is a further object of this invention to provide a regeneration system which is capable of raising the exhaust gas temperature to levels sufficient to cause incineration of the trapped particulate without the use of an auxiliary burner.